How do I complete my animation so that I may add nodes in composting?
Hey I had the same problem, here's how it worked out: 
I guess you're pressing f3 when he says 'search' for the denoiser, and then denoise animation pops up, right?


You need to hit shift+a, then click on 'search' in the menu that pops up.


You should find an option simply called 'denoise', not 'denoise animation'

Hope this helps!